The basic problem that diabetic patients have relates to the transfer of sugar, contained in the blood, across cell membranes. This in turn makes it difficult for the body to maintain sugar levels in the blood at the correct level. In the treatment of diabetes, patients regularly check blood glucose levels using a self-testing kit. By comparing the result of a self-test with the blood glucose level considered normal, a patient is able to estimate the amount of insulin that should be taken to keep the blood glucose level near normal. Too much blood sugar (e.g. due to the patient injecting too little insulin) or eating more than the prescribed amount is defined as hyperglycemic while too little blood sugar (e.g. due to the patient injecting too much insulin) is defined as hypoglycemic. These are considered to be short-term complications of diabetes and can cause acute symptoms or be a factor in the development of long-term complications. Diabetic patients can also suffer problems arising from their condition that only become apparent in the longer term. These problems are caused by excessive levels of sugar in the blood that result in, among other causes, sugar combining with protein to form glycosylated protein. Glycosylated protein is substantially insoluble and gives rise to thickening of the walls of veins and arteries, and thickening of the myelination of nerves.
One particular form of glycosylated protein is glycosylated hemoglobin. As glycosylated hemoglobin tends to remain in the blood, it provides an excellent indication of the level of glycosylated protein in the blood and therefore of the effectiveness of the treatment regime a patient has been following, as well as indicating how well the patient is following that regime.
Glycosylated hemoglobin includes three components; namely, HbA1a, HbA1b, and HbA1c. It has been shown that a normal level of HbA1c in a diabetic patient's blood is a good indication that the treatment regime is effective and the risk of secondary complications of diabetes is low. The level of HbA1c in a healthy person's blood is between 4% and 6% of the total hemoglobin while in a diabetic person the level may be significantly higher (e.g. greater than 8%). It is generally sought to reduce the level of HbA1c in a diabetic patient's blood to between 6% and 7%. The HbA1c level reflects the idiosyncratic (i.e. patient-specific) effectiveness of blood glucose treatment over a period of several months preceding the HbA1c measurement. The HbA1c level is commonly measured by laboratory tests in order to provide information related to the long term effectiveness of diabetes treatment.
While HbA1c protein levels provide valuable information, HbA1c levels are measured infrequently for typical patients and give no indication as to the variability associated with a patient's glycemic control or the propensity for hypoglycemia or hyperglycemia. For example, a patient may have an acceptable HbA1c level ranging between 4% and 7% but may have frequent hypoglycemic and/or hyperglycemic episodes because such episodes are not reflected in an HbA1c level.
Information relating to variability can be useful to a patient with diabetes or their clinician for a number of reasons. High variability can indicate brittle diabetes and may also indicate that a patient is not compensating for hypoglycemia and hyperglycemia adequately. A high variability may also indicate an increased risk of severe hypoglycemia, diabetic ketoacidosis and other acute complications, and therefore a patient with higher variability should be monitored more closely and this information should be taken into account when adjusting a therapeutic regimen.